1. Field of the Invention
The invention relates to a method for the making of heteroepitaxial thin layers and, more specifically, for the making of layers of different types of semiconductor materials. The invention also relates to the application of this method to the making of electronic and optoelectronic devices.
The invention can be used to obtain thin layers with a low density of defects, on a substrate that is also monocrystalline and that, in principle, has a distinct nature, by using seeds of a third material.
For example, the method according to the invention can be used to obtain thin layers of InP of high crystalline quality on a silicon substrate, using GaAs seeds. Furthermore, the method according to the invention can be used to obtain particular structures and associations of components (lasers, photodiodes, gun diodes etc.) based on III-V type material on a silicon substrate.
2. Description of the Prior Art
The heteroepitaxial growth of thin layers of III-V type compounds of high crystallographic quality on a silicon substrate enables the association of semiconductors having direct gaps and high mobility with a material that is technologically well mastered.
The result thereof is an extremely vast range of applications, in fields such as integrated optoelectronics (lasers and photodiodes with associated commands), optical telecommunications, power components made of III-V type materials, optical connection systems on silicon chips etc.
From a technical point of view, the growth of III-V type components on silicon is done by MBE (Molecular Beam Epitaxy) or MOVPE (Metalorganic Vapor Phase Epitaxy), which gives epitaxially grown thin layers having densities of dislocations greater than 10.sup.6 /cm.sup.2 (cf. S. F. Fang et al. in J. Appl. Phys., 68, R31-190), with which it is impossible to make optical components (such as lasers and photodiodes) having acceptable longevity.
Furthermore, while the epitaxy of GaAs on Si by MBE or MOVPE is relatively controlled, that of InP is very difficult to implement, for nucleation on Si takes place only at low temperature.
Consequently, it is difficult to decompose phosphine (PH.sub.3) when working with "source gas" MBE or else phosphine and metalorganics (trimethyl and triethylindium) when using MOVPE or MOMBE (Metalorganic Molecular Beam Epitaxy). Finally, the use of phosphorus at low temperature in standard MBE raises problems of pumping. In all cases, the InP layers show dislocation levels of over 10.sup.6 /cm.sup.2 as indicated here above.
The French patent applications Nos. 88 04437 and 88 04438 describe methods of growth that enable notable improvements in the quality of the heteroepitaxial layers of III-V materials on a silicon substrate.
Improvements to these methods have been described in the patent applications Nos. 90 12443 and 91 12352.
In the different documents referred to here above, the heteroepitaxy related to a material B (for example GaAs) on a substrate A (for example Si).
The present invention relates to a method for obtaining a material C that is monocrystalline and without defects (for example InP) from seeds of a material B (for example GaAs) on a substrate of a material A (for example silicon).
Taking the examples of materials indicated here above, the invention enables a "directed" growth of InP with high crystallographic quality on silicon, using very poor quality GaAs seeds. Furthermore, the step of direct growth (MBE or MOVPE) of InP on Si, which is very difficult to implement, is eliminated.